Demand on mobile data service continues to grow dramatically in the recent years. The growth in demand is driven by modern portable handheld devices, such as smart phone, tablet PC, portable router etc. The growth in demand is also driven by new applications, such as streaming video, e-book, online gaming etc. Studies have shown that the demand for mobile data service is expected to grow more than fifty times from year 2008 to 2013.
To meet this fast growing demand in mobile data service, various network operators are developing new technologies and defining new standards for the next generation wireless networks to achieve much higher peak transmission rate. For example, 1 Gbps peak transmission rate is required by ITU-R for IMT-Advanced systems in the 4th generation (“4G”) mobile communications systems. 1 Gbps peak transmission rate in wireless networks can provide users similar experience as in wireline networks, and it is sufficient to satisfy most applications on the Internet today and in the near future.
While peak transmission rate is no longer a critical problem after 4G era, network capacity is likely to be exhausted very soon in the next few years. Not only traffic demand is growing dramatically (i.e., >50× in 5 years), but also the improvement on average cell spectral efficiency is very limited from 3G to 4G era (i.e., <10×). In addition, the available spectrum resource is also limited. Network capacity will still be exhausted very soon even all the networks are upgraded with 4G air interface. This problem in fact already happens in some areas. Therefore, capacity exhaustion is anticipated to be the most critical problem during 4G and beyond 4G (B4G) era.
While the demand on wireless communication service continues to increase, the demand on broadband access may not always require mobility support. In fact, studies have shown that only a small fraction of users demand on simultaneous mobile and broadband access. Therefore, in addition to cellular networks, there are other networks able to deliver information to mobile users, with or without mobility support. In most geographic areas, multiple radio access networks (RANs) such as E-UTRAN and WLAN are usually available. Furthermore, wireless communication devices are increasingly being equipped with multiple radio transceivers for accessing different radio access networks. For example, a multiple radio terminal (MRT) may simultaneously include Bluetooth, WiMAX, and WiFi radio transceivers. Thus, multi-radio integration becomes more feasible today and is the key to help user terminals to explore more bandwidth available from different radio access technologies and achieve better utilization of scarce radio spectrum resources.
Multi-radio integration needs to be achieved from two perspectives. From the network perspective, much research has already been done since 3G era on inter-networking for traffic routing and offloading in the backhaul (i.e., wireline) network. On the other hand, from the device perspective, certain research has just been initiated to investigate how different radio access networks can interwork with each other to prevent mutual interference. However, it has not been well studied on how different radio interfaces of the same device can interwork to improve transmission efficiency, and how radio access networks can help the device with shared components for different radio interfaces to work well together.